1. Field of the Invention
The present invention generally relates to a flat display, and more particularly, to a transflective liquid crystal display (TR LCD) with single cell gap mode.
2. Description of Related Art
An LCD can be roughly categorized into three types: transmissive type, reflective type and transflective type, wherein the TR LCD able to work by using both a backlight source and an external light source is preferably used in portable electronic products such as mobile phone, personal digital assistant (PDA) and e-book and so on. Based on this advantage, the TR LCD is paid attention to by the relevant manufactures.
In general, a TR LCD can be further categorized into a TR LCD with single cell gap mode and a TR LCD with dual cell gap mode. Since the TR LCD with single cell gap mode is advantageous in simpler fabrication than the TR LCD with dual cell gap mode and lower production cost, so that the TR LCD with single cell gap mode is the most preferable one used in various portable electronic products.
FIG. 1 is an equivalent circuit diagram of a single pixel 101 in a conventional TR LCD 100 with single cell gap mode and FIG. 2 is a graph diagram showing a characteristic curve TC of transmittance vs. pixel voltage (or termed as ‘transmissive Gamma curve’) of the transparent area TA and a characteristic curve RC of transmittance vs. pixel voltage (or termed as ‘reflective Gamma curve’) of the reflection area RA within the pixel 101 of FIG. 1. Referring to FIGS. 1 and 2, the pixel 101 has a transparent area TA and a reflection area RA, wherein the transparent area TA has a pixel transistor T, a first liquid crystal capacitor CLC1 and a storage capacitor CST disposed wherein, while the reflection area RA has a coupling capacitor CC and a second liquid crystal capacitor CLC2.
The gate of the pixel transistor T is coupled to a scan line 103 and the source of the pixel transistor T is coupled to a data line 105. The drain of the pixel transistor T is coupled to the first terminals of the first liquid crystal capacitor CLC1, the storage capacitor CST and the coupling capacitor CC. The second terminals of the first liquid crystal capacitor CLC1 and the storage capacitor CST are coupled to a common electrode CE to receive a common voltage Vcom. The second terminal of the coupling capacitor CC is coupled to the first terminal of the second liquid crystal capacitor CLC2 and the second terminal of the second liquid crystal capacitor CLC2 is coupled to the common electrode CE.
The conventional transflective display with single cell gap mode provides the reflection area RA with a divided voltage of the coupling capacitor CC and the provided divided voltage serves as the required pixel voltage. However, it can be seen from FIG. 2 that due to the mismatch between the characteristic curve TC of the transparent area TA and the characteristic curve RC of the reflection area RA of the pixel 101, so that the transmissive displaying effect and the reflective displaying effect of a conventional TR LCD 100 with single cell gap mode are unable to simultaneously achieve the optimization.
In order to make the transmissive displaying effect and the reflective displaying effect of the TR LCD 100 with single cell gap mode simultaneously achieve the optimization, a better solution was provided by the inventor of the present invention in U.S. patent application Ser. No. 12/571,446, which all disclosures are incorporated herein by reference herewith, referring to FIGS. 3 and 4. FIG. 3 is an equivalent circuit diagram of a single pixel 301 in another conventional TR LCD 300 with single cell gap mode and FIG. 4 is a graph diagram showing a characteristic curve TC of transmittance vs. pixel voltage of the transparent area TA and a characteristic curve RC of transmittance vs. pixel voltage of the reflection area RA within the pixel 301 of FIG. 3. In FIGS. 3 and 4, the pixel 301 has a transparent area TA and a reflection area RA, wherein the transparent area TA has a pixel transistor T, a first liquid crystal capacitor CLC1 and a storage capacitor CST, while the reflection area RA has a coupling capacitor CC, a second liquid crystal capacitor CLC2 and a compensation capacitor CC2.
The gate of the pixel transistor T is coupled to a scan line 303 and the source of the pixel transistor T is coupled to a data line 305. The drain of the pixel transistor T is coupled to the first terminals of the first liquid crystal capacitor CLC1, the storage capacitor CST and the coupling capacitor CC. The second terminals of the first liquid crystal capacitor CLC1 and the storage capacitor CST are coupled to a common electrode CE to receive a common voltage Vcom1. The second terminal of the coupling capacitor CC is coupled to the first terminal of the second liquid crystal capacitor CLC2 and the second terminal of the second liquid crystal capacitor CLC2 is coupled to the common electrode CE. The first terminal of the compensation capacitor CC2 is coupled to the second terminal of the second terminal of the coupling capacitor CC and the second terminal of the compensation capacitor CC2 is coupled to a reference voltage line 307 so as to receive a reference voltage signal Vref with time-varying signal property.
It can be seen from FIG. 4 that the newly added compensation capacitor CC2 disposed in the reflection area RA of the pixel 301 and coupled to the reference voltage signal Vref is helpful for the inter-match between the characteristic curve TC of the transparent area TA and the characteristic curve RC of the reflection area RA of the pixel 301, and thereby, the transmissive displaying effect and the reflective displaying effect of the TR LCD 300 with single cell gap mode are able to simultaneously achieve the optimization.
However, the second terminals of all the compensation capacitors CC2 respectively in the reflection area RA of each pixel of the TR LCD 300 with single cell gap mode are coupled to the reference voltage line 307 to receive the reference voltage signal Vref, so that the TR LCD 300 with single cell gap mode is limited to adopt the row inversion panel-driving approach and the frame inversion panel-driving approach and forbidden from adopting the column inversion panel-driving approach and the dot inversion panel-driving approach, which brings a disadvantage of lower general purpose of design with the TR LCD 300 with single cell gap mode.